1. Field of the Invention
The present invention relates generally to disk drives, and in particular to a disk drive including a flex circuit assembly with an integrated circuit device attached to a base film with an underfill portion and sealed with a glob top portion.
2. Description of the Prior Art
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly includes at least one transducer head, typically several, for reading and writing data from and to the disk. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The head stack assembly includes an actuator assembly, at least one head gimbal assembly, and a flex circuit assembly. A conventional “rotary” or “swing-type” actuator assembly typically includes a rotary actuator having an actuator body. The actuator body has a bore and a pivot bearing cartridge engaged within the bore to facilitate rotational movement of the actuator assembly between limited positions about an axis of rotation. A coil support extends from one side of the actuator body. An actuator coil is supported by the coil support and is configured to interact with one or more permanent magnets to form a voice coil motor. One or more actuator arms extend from an opposite side of the actuator body. Each head gimbal assembly includes a transducer head, typically a magneto-resistive (“MR”) head, which is distally attached to each of the actuator arms. Each magnetic disk includes opposing disk surfaces. Data may be recorded along data annular regions on a single disk surface or both. As such, the head stack assembly may be pivoted such that each transducer head is disposed adjacent to the various data annular regions from adjacent to the outer diameter to the inner diameter of each disk.
The flex circuit assembly is configured (1) to supply current to the actuator coil and (2) to carry signals between the transducer heads and the printed circuit board assembly. The flex circuit assembly includes a flex circuit (also referred to as a flex circuit cable), an integrated circuit, and a flex circuit connector. The flex circuit includes a dynamic loop portion that is supported by a cable guide. This configuration permits relatively free rotation of the overall head stack assembly.
At one end of the flex circuit there is provided a mounting portion which is attached to a side of the actuator body. Adjacent to the mounting portion, the flex circuit contains a terminal pad portion for connecting a plurality of electrically conductive traces embedded within the flex circuit to electrical connectors, such as insulated wires. The wires extend along the actuator arms to each transducer head for transmitting data signals to and from the transducer heads. At an opposing end of the flex circuit, there is provided a flex circuit connector that is attached to the disk drive base and electrically connected to the printed circuit board assembly.
The flex circuit typically includes a base film, a plurality of electrically conductive traces and a cover film. The base film and the cover film are commonly formed of a polyimide material. The electrically conductive traces are formed upon base film. The cover film is then selectively disposed over the metal traces and the base film for electrically insulating the traces. Adjacent to the mounting portion of the flex circuit, the cover film includes an opening. Within this opening the integrated circuit in the form of an integrated circuit device is attached to the base film and is electrically connected to the traces. The integrated circuit device includes a preamplifier for enhancing signals passed from the transducer heads.
One type of integrated circuit devices includes a die which is electrically connected to a plurality of solder bumps disposed along a bottom face of the device. The solder bumps correspond to pads formed in the traces. When attaching the integrated circuit device to the base film, an underfill material is commonly used. The amount of underfill material is carefully dispensed as it is considered to be relatively expensive. While the opening formed in the cover film allows access to the traces for the attachment of the integrated circuit device, the metal traces are exposed at such region between the underfill material and the opening. In a follow-up touch up process, the same underfill material is typically used to cover these exposed traces. Accordingly, there is a need in the art for an improved flex circuit assembly configuration in comparison to the prior art.